Clutch pack braking is a well-established method of braking vehicles and refers to using clutch packs in the transmission system to slow or brake a vehicle. Clutch pack braking is usually performed by slipping one clutch pack while locking the other clutch pack. This technique concentrates all of the energy in the slipping pack, or if both packs are slipped, can produce unpredictable slipping in both clutch packs. Also, if part throttle braking is attempted, clutch pack braking can stall the vehicle engine by turning the torque converter turbine in the transmission system backwards and overloading the engine. Thus a vehicle operator currently has to use a brake pedal to stop a vehicle at higher speeds.
Energy is wasted in power shift transmissions due to large torque converter slippage at low truck speeds. This usually happens when the vehicle is generating maximum pushing forces. This energy loss can be up to 100 percent of engine power.
The present invention addresses this and other problems associated with the prior art.
A transmission system includes a Central Processing Unit (CPU) that controls the turbine speed of a torque converter by reducing engine speed and then slipping two clutch packs at the same time. The CPU reduces the engine speed to idle, regardless of the specific throttle request made by the vehicle operator. The CPU then controls clutch pack activation pressure to obtain the optimum split of energy between the two clutch packs during braking. By sharing braking energy between the two clutch packs, conventional clutch packs can be used for high-speed vehicle direction reversals and high-speed vehicle braking.
In another aspect of the transmission system, energy loss is reduced during high Draw Bar Pull conditions. The engine speed is modulated to trim energy peaks at low speeds. An additional transmission gear reduction restores the lost pushing forces while generating less heat in the torque converter. A radiator air-to-oil cooling system extracts the extra heat generated when the vehicle is pushing loads and extends the normal allowable pushing time for the vehicle.